Use treble_linker_namespace instead of treble.

More specific. Treble is being removed.

Bug: 62019611
Test: manual
Change-Id: I94c21c6a5cb6a258bfb36a0b7da23abdc73a67fb

libc/Android.bp

@@ -1419,8 +1419,8 @@ cc_library_static {
         },
     },
     product_variables: {
-        treble: {
-            cflags: ["-D__ANDROID_TREBLE__"],
+        treble_linker_namespaces: {
+            cflags: ["-DTREBLE_LINKER_NAMESPACES"],
         },
     },
     cppflags: ["-Wold-style-cast"],

libc/bionic/__bionic_get_shell_path.cpp

@@ -40,7 +40,7 @@ static const char* init_sh_path() {
    * in $PATH for the vendor shell, simply return the system shell.
    */
 
-#ifdef __ANDROID_TREBLE__
+#ifdef TREBLE_LINKER_NAMESPACES
   /* look for /system or /vendor prefix */
   char exe_path[strlen(VENDOR_PREFIX)];
   ssize_t len = readlink("/proc/self/exe", exe_path, sizeof(exe_path));